Such an electric motor circuit is known, for instance, from the European patent publication EP 1 393 975. By activating the electric motor through the circuit, the mirror adjustment mechanism can pivot a mirror housing relative to a bodywork on which the mirror housing is mounted. This allows the user of a motor vehicle, from the driver's space, to cause the mirror housing to fold in or fold out between a working position in which the mirror housing is oriented substantially transversely relative to the bodywork and a folded-in position in which the mirror housing is oriented rearwards and alongside the bodywork. For instance when maneuvering during parking, the driver can then, to reduce the width of the vehicle, bring the mirror housing from the working position to the folded-in position.
Upon reaching an end position, such as the working position or the folded-in position, the mirror housing cannot pivot further relative to the bodywork, so that the operation of the electric motor is blocked. When the electric motor remains switched on, relatively high supply currents occur in the windings of the motor, which may drastically reduce the life of the motor. To obviate high currents in the electric motor, the electric motor circuit is further arranged to switch off the electric motor when the electrical supply current is greater than a predetermined critical level.
In the circuit as described in EP 1 393 975, the current sensor is integrated in the electrical switch which is designed as a FET. A relatively high current results in a rise of the voltage of the base of a bipolar transistor, which thereby becomes conductive, so that an associated current branch starts to carry current. As a result, the potential on the gate of the FET falls, so that the FET does not pass any electrical current anymore. Since the FET is connected in series with the electric motor, the electric motor switches off.
For the above-mentioned bipolar transistor to be rendered conductive, a sufficiently high electrical voltage needs to be provided to the base. Before a sufficiently high voltage has been built up, the electrical supply current reaches a relatively high value and/or the conducting path of the FET has a relatively high resistance. The object of the circuit is precisely to avoid the first situation. However, the second situation, that is, designing the FET with a relatively high resistance, is also unwanted, since in that case less effective power becomes available to the electric motor itself.